Avoiding Adverse Costs: The Perils of Medico-Legal Experts Opining Beyond Their Sub-Specialty in Capacity Assessments

In the complex landscape of UK litigation, the integrity and admissibility of expert evidence are under increasing scrutiny. Solicitors, barristers, and local authority legal teams frequently rely on medico-legal experts to provide robust, evidence-based opinions, particularly in cases involving capacity assessments. However, a significant and often overlooked risk arises when an expert attempts to opine outside their specific sub-specialty, leading to challenges to their evidence, delays, and crucially, the potential for adverse costs. Understanding the importance of precise expert instruction, therefore, becomes paramount.

This article explores the critical need for experts to operate strictly within their sub-specialty when assessing capacity, highlighting the medico-legal implications for cases across criminal, family, personal injury, and, most prominently, Court of Protection proceedings. It is in this context that the risk of expert witness scope adverse costs becomes particularly pertinent, impacting litigation strategy and client outcomes.

The Clinical Nuance of Capacity Assessments: More Than a Checklist

Determining an individual’s capacity is a nuanced clinical and legal process, not a simple diagnostic label. In the UK, capacity assessments are governed by the Mental Capacity Act 2005 (MCA 2005), which establishes five core principles:

1. A person must be assumed to have capacity unless it is established otherwise.
2. A person is not to be treated as unable to make a decision unless all practicable steps to help them to do so have been taken without success.
3. An unwise decision does not, of itself, mean a person lacks capacity.
4. An act done or decision made under the MCA 2005 for or on behalf of a person who lacks capacity must be done or made in their best interests.
5. Before the act is done or the decision is made, consideration must be given to whether the purpose can be as effectively achieved in a way that is less restrictive of the person’s rights and freedom of action.

Central to these principles is the two-stage test for assessing capacity: firstly, whether there is an impairment of, or a disturbance in the functioning of, the mind or brain; and secondly, whether that impairment or disturbance makes the person unable to make a specific decision when they need to. This decision-specific nature is crucial, meaning a person might have capacity for one decision but not another.

Different types of capacity assessments arise in medico-legal practice:

• Litigation Capacity: The ability to understand the proceedings, give instructions to solicitors, and make decisions about the case (relevant across civil, family, and criminal proceedings).
• Testamentary Capacity: The capacity required to make a valid will, typically assessed against the common law test in Banks v Goodfellow (1870).
• Capacity to make decisions about care, residence, finance, or medical treatment: Primarily dealt with under the MCA 2005 in the Court of Protection.

Each type requires a deep understanding of the relevant legal test, combined with specialist clinical insight into the underlying medical or psychiatric condition that may be causing the impairment. This demands more than general medical knowledge; it necessitates sub-specialty expertise to accurately identify and assess the precise nature and functional impact of complex conditions.

Legal Relevance and the Pitfall of Misdirected Expertise

Expert evidence on capacity is routinely required across various legal domains. In the Court of Protection, experts complete the COP3 form, providing a declaration of capacity. In personal injury claims, capacity to manage damages or instruct solicitors is often critical. Family proceedings may require assessment of parental capacity, while criminal matters might touch upon fitness to plead. Regardless of the jurisdiction, CPR Part 35 (and analogous rules) mandates that experts must define the scope of their expertise and operate strictly within it.

In medico-legal practice, it is widely recognised that the most common pitfalls arise when an expert, though qualified in a broad field, ventures into an area requiring a specific sub-specialty. For example:

• A general adult psychiatrist attempting to assess capacity in a case predominantly involving complex neurodegenerative disease (e.g., specific dementias or acquired brain injury), rather than an old age psychiatrist or a neuropsychiatrist.
• A learning disability specialist asked to opine on capacity where the primary impairment is a result of advanced vascular dementia, which falls outside their core training.
• A medical expert (e.g., a neurologist or geriatrician) attempting to provide opinions on complex psychiatric conditions without specialist psychiatric training.

Such scenarios create a significant risk. An expert opining outside their specific sub-specialty may lack the in-depth diagnostic understanding, the tools for precise assessment, or the experience to accurately interpret the functional impact of a particular condition on decision-making. This directly contributes to the risk of expert witness scope adverse costs.

Adverse Costs: When Expert Evidence Fails the Test

When an expert’s report or oral evidence is found to be outside their demonstrated expertise, the consequences can be severe for the instructing party. The court may:

• Give the evidence little or no weight: If the expert lacks specific sub-specialty knowledge, their opinions may be challenged as unconvincing or unreliable.
• Exclude the evidence entirely: The court may rule that the expert is not qualified to give an opinion on a particular aspect, rendering the report inadmissible.
• Order new expert evidence: This causes significant delays, additional costs, and undermines the instructing party’s case strategy.
• Make a costs order against the instructing party: Wasted costs, including the expense of the initial inadequate report, the time taken to challenge it, and the costs of instructing a new expert, can be substantial. In some egregious circumstances, a third-party costs order might even be considered against the expert, though this is rare. However, the instructing solicitor bears the primary burden of ensuring appropriate expert instruction, and therefore carries the bulk of the risk.

These scenarios highlight how misjudging an expert witness scope adverse costs can be a direct result of inadequate scrutiny during the expert selection process. The instructing solicitor has a duty to ensure the expert is appropriately qualified for the specific task at hand, not just generally qualified in a broad discipline.

The Role of the Specialist Expert Witness in Capacity Assessments

A specialist medico-legal expert, operating within their defined sub-specialty, provides invaluable assistance to the court. Their report will typically:

• Demonstrate specialist knowledge: Clearly articulate the underlying medical/psychiatric condition, its specific diagnostic criteria, and typical presentation.
• Apply the correct legal test: Precisely align the clinical findings with the two-stage test of the MCA 2005 or other relevant legal tests (e.g., Banks v Goodfellow).
• Provide decision-specific assessments: Address the specific decision(s) in question (e.g., capacity to manage finances, capacity to choose residence, capacity to consent to medical treatment).
• Rely on comprehensive information: Integrate all relevant medical records, social care reports, witness statements, and any previous assessments.
• Clearly state limitations: A good expert will transparently state any limitations to their expertise or the scope of their assessment.
• Offer robust, defensible opinions: Provide reasoning that can withstand scrutiny, including cross-examination.

By ensuring an expert’s sub-specialty aligns perfectly with the clinical questions, solicitors can significantly strengthen their case, avoid evidentiary challenges, and prevent the financial penalties associated with expert witness scope adverse costs.

Practical Guidance for Solicitors

To mitigate the risks outlined above, solicitors should adopt a proactive and meticulous approach when instructing medico-legal experts for capacity assessments:

• Identify the precise clinical question: Beyond merely ‘capacity’, what is the specific underlying condition impacting capacity? Is it a neurodevelopmental disorder, an acquired brain injury, a complex psychiatric illness, or a specific type of dementia?
• Scrutinise expert CVs: Look beyond general qualifications. Does the expert have specific sub-specialty training, accreditations, and experience directly relevant to the client’s condition (e.g., old age psychiatry, neuropsychiatry, learning disability psychiatry, forensic psychiatry)?
• Provide comprehensive instructions: Furnish the expert with all relevant documentation at the outset. This includes medical records, previous capacity assessments, social care reports, witness statements, and a clear list of specific questions to be addressed.
• Clarify the scope: Ensure the letter of instruction explicitly details the specific capacity to be assessed and the legal test to be applied.
• Communicate openly: Maintain dialogue with the expert. If the expert identifies that the case falls outside their specific sub-specialty, or requires input from another specialist, heed that advice promptly.
• Consider multi-disciplinary input: For particularly complex cases, a multi-disciplinary approach involving experts from different sub-specialties (e.g., a neuropsychiatrist and a neuro-psychologist) may be warranted.

Selecting a medico-legal expert whose sub-specialty precisely aligns with the complex clinical questions in a capacity assessment is not merely good practice; it is a vital safeguard against litigation strategy pitfalls and the risk of adverse costs. Early and precise instruction of the right specialist expert can prove to be the most cost-effective and legally sound approach in the long term.

Specialist medico-legal assessment from an experienced expert witness can be pivotal in cases of this nature.